1. Field of the Invention
The present invention relates to an image display apparatus and, particularly to an image display apparatus of dot-matrix type practiced as a CRT display unit or a liquid crystal display unit.
2. Description of the Prior Art
An example of this type of display apparatus shown in FIG. 1 is disclosed in U.S. Pat. No. 4,520,358. The arrangement shown includes a central processing unit and associated circuitry (will be termed simply "CPU" hereinafter) 1, an image display memory for holding image and color information (will be termed simply "V-RAM" hereinafter) 2, a dot-matrix image display device such as a CRT unit or liquid crystal panel and associated circuitry (will be termed simply "display device" hereinafter) 3, and a display control circuit 4 for controlling the V-RAM 2 and display device 3.
In the above arrangement, when an image is displayed on the display device 3, the CPU 1 writes the image information into the V-RAM 2. The image information written in the V-RAM 2 is read out sequentially under control of the display control circuit 4 and delivered to the display device 3. Upon receiving the information, the display device 3 display it as a pattern of dots in specified brightness and colors. The V-RAM 2 has its information storage locations corresponding to the dots on the display device 3 simply on a bit-by-bit basis, and a bit pattern which the CPU 1 has written into the V-RAM 2 is just transferred to the screen of the display device 3, and an assembly of dots in respective brightness is visualized as an image.
However, the conventional image display system constructed as described above does not operate correctly for displaying an image provided by the CPU 1 when it connects with a display device having a different performance than that of the display device which matches the application program run by the CPU 1. For example, if a personal computer system is once constructed including a monochrome liquid crystal display panel, it cannot run an application program oriented to the color CRT display device.